The present invention relates to self-propelled vehicles which are adapted to utilize wind power as a second source of energy for propulsion purposes.
It is recognized that the modern automobile is in need of significant changes to reduce substantially its requirement for fuel. Various efforts in this direction have been undertaken, such as providing three-wheeled arrangements which save weight and rolling resistance compared with vehicles having four wheels; utilizing narrow vehicle bodies seating two people in tandem so as to reduce drag by reducing the frontal area of the vehicle; utilizing vertical airfoils or fins to provide forward thrust in the presence of a crosswind. These concepts are known in the prior art and are disclosed, for example, in U.S. Pat. No. 4,117,900, patented Oct. 3, 1978 in the name of Amick. However, further advancements are still required to meet the needs of the public for energy-efficient vehicles that have optimum dimensions and driving performance commensurate with lower fuel consumption.
Conventional automobiles with four wheels are to some extent inherently unstable in crosswinds, and this problem becomes more acute when steps are taken to reduce the weight of the vehicles in the interest of fuel economy. Similarly, aerodynamic drag of conventional automobiles is substantially greater than desirable and is a factor contributing to these vehicles having a higher fuel consumption than is necessary. Vehicles such as are disclosed in U.S. Pat. No. 4,117,900 have light weight characteristics and have design characteristics which materially reduced the aerodynamic drag when compared with conventional automobiles, but further advancements are required. In particular, there is still a need for improvements in conventional automobiles or in vehicles of the type disclosed in the aforesaid patent, wherein the vehicles can be made very light in weight and still have good steering characteristics in a crosswind and on slippery roads, and wherein the vehicles also are constructed to avoid extending the overall lengths excessively for the purpose of minimizing drag.
Recent wind-tunnel tests of a model of an energy-efficient motorcycle of a desirable length designed according to the principles of the aforesaid patent revealed a flow separation problem. The energy-efficient motorcycle model that was tested consisted of a streamlined fuselage containing a single nose wheel, with horizontal struts extending laterally from both sides of the fuselage to rear wheels partially enclosed within the lower portions of vertical airfoils or fins.
The wind tunnel tests of this configuration revealed boundary-layer separation on the rear part of the fuselage, due to the adverse pressure gradient field of the rear part of each vertical airfoil combining with that of the adjacent fuselage. This interference between vertical airfoil and fuselage occurred because of their relative proximity compared with the airfoil size, in this configuration.
Boundary-layer separation is undesirable since it results in a significant increase in drag. The airfoil boundary layer did not separate when the fuselage boundary layer did, even though the airfoil boundary layer is exposed to nearly the same adverse pressure gradient, because it is thinner, having developed over a shorter distance. Thus, there is a need for further advancement in the art if greater fuel economy is to be realized.